Cables for telecommunication, such as glass fibre cables in particular, are seen as the basis of a communication network. Efficiency requires that use be made of already existing pipe systems in the ground for the purpose of laying such a new cable network. A sewer forms a very suitable pipe network here. The sewer system in cities comprises a network of main sewers running below streets to which individual house sewers or house sewer connections are connected. The main sewer has a cross-section sufficiently large for a robot, and there are sewer drains through which a glass fibre cable can be introduced into the sewer. A method for laying a glass fibre cable in such a main sewer is per se known from EP 1868020.
In for instance an outlying area outside a city the number of connections to the sewer per kilometre is low. This causes too little flow in a normal sewer for the purpose of draining the sewer content. Use is thus often made of a pressure sewer. This is a pipe with a small diameter which is operated with a pressure pump such that the sewer content is actively pumped away. The house connection of a dwelling to a pressure sewer effectively consists of a catch pit which is emptied on a regular basis by pumping to the pressure sewer. As a result it is not possible to introduce a robot into an existing pressure sewer for the purpose of laying a glass fibre cable. Nor is it possible to simply open the pressure sewer in order to make a connection. It is further not possible to draw the glass fibre cable to a dwelling via a house connection of the sewer, but a bridging is necessary between a connection point in the pressure sewer and a further connection to the dwelling, such as for instance an inspection well.
The British patent application GB 2312995 discloses a solution for introducing a glass fibre cable into a medium conduit for a medium under pressure. This relates particularly to a water conduit or a gas conduit, with a pipe as primary component of the system. A cable is introduced into the pipe here together with a pulling member. The pulling member will pull the cable through the pipe. A spreadable and collapsible pulling member is used for a medium under pressure. The pulling member is provided for this purpose with suitable means, such as a collapsible screen. The screen absorbs the pressure and is in this way carried along with the flow in the pipe. Situated at a first longitudinal position where the cable has to be taken out of the medium conduit is a cable outlet. Situated at a second longitudinal position located a little further along (i.e. downstream) is a cable inlet with which the cable can once again be introduced into the pipe of the medium conduit. According to this British patent application, taking out the cable serves the particular purpose of circumventing obstacles in the medium conduit. In the case of a gas conduit this is for instance a closing valve.
It is however a drawback of the known medium conduit that the cable is situated inside the medium conduit at a position which cannot be determined. When the medium conduit transports something other than gas or liquid, such as in particular a pressure sewer, this can easily result in highly undesirable blockages. Not only must a blockage be cleared as quickly as possible, a blockage is also difficult to trace since the conduit is located under the ground and is optically non-transparent.